This was an answer to a question posted on the YW list.  If you want more info, please feel free to e-mail me! -CW
For your your next combined activity, why not make it a get-to-know-you night with different games and mixers to get the kids to know eachother better as friends.  Perhaps you could have a list of things for them to fill out, and then they can go through them and pick out their ideal friend.

For example, on a sheet of paper, have different likes/dislikes for the kids to fill in.  They are not allowed to put their name or gender on the papers, but you should have a number that corresponds to the person's name on a seperate list.

Things you could include on the list:

Post the pages on a wall, and have the kids go through and pick out their top five "ideal friends". They can list the numbers from the pages on an index card - for their eyes only.  Near the end of the evening, read the list of names and numbers.

They will be shocked and/or surprised that some of their choices are of the opposite sex.  Then, after all of the fun and games, have some newly married couples (and some not-so-newly married) come in and talk about the importance of being friends before and during your marriage.

This way, you cover the importance of building relationships for the younger kids, as well as the importance of friendship with the people you date for the older set - without focusing on the dating relationship.